Securing DeCordova Bend Dam’s future
The Brazos River Authority broke ground for Lake Granbury in December 1966.
Three years later, the DeCordova Bend Dam was complete. Now nearly 60 years old, the Tainter gates used for passing floodwater, still original to the dam, are under the microscope as staff determines the best way to ensure the longevity of the important infrastructure.
Could that mean total gate replacement?
It’s an option.
It’s all about preventative maintenance, said Dylan Mayfield, BRA Lake Granbury reservoir manager. This project and review are all about continuing the safe operation and integrity of the dam, Mayfield said.
“With any aged structure, we’re looking forward and trying to get out ahead of any issues,” he said.
It’s like an old car, said BRA Project Engineer Wesley Williams. You can keep replacing parts, but at some point, it may be cheaper to buy a new one. This project is studying which route is best.
The DeCordova Bend Dam is a slab-and-buttress type structure, sometimes called an Ambursen Dam, named after the original designer. Holding back a storage capacity of about 136,326 acre-feet of water, the dam is 2,200 feet long and 84 feet high and has 16 Tainter-style gates, each 35 feet tall by 36 feet wide.
The project to review the dam and its condition includes several phases. The first phase focused partly on a comprehensive evaluation of the gates and all the associated components and equipment necessary to use and support them, said BRA Project Manager Lacey Darr. The next phase will further refine both options of either rehabilitation or replacement up to 30% design. Ultimately, the project will identify the best route forward: rehabilitating the existing Tainter gates or fully replacing them. The study will compare the options, cost, constructability, risk, and long-term performance before committing to a path forward, she said.
“These Tainter gates are an important part of the dam’s infrastructure and how we manage water supply and flood operations,” Darr said. “We take on projects like this to ensure every part of our resources are operating effectively and supporting our goals as intended.”
Since the review is examining all parts of the dam, it will also look at the hoist trolley system housed on top of DeCordova Bend Dam.
The hoist trolley system is older than the dam and was purchased when the dam was constructed, Mayfield said. Tracks run across the top of the dam, and the trolley is used to place and remove stoplogs. These stop logs, once stacked on top of one another in front of a gate, create an almost completely waterproof barrier allowing staff easy access to the portion of the Tainter gate normally underwater. This facilitates gate inspections, maintenance, and repairs.
It takes almost all day to install enough stop logs to block off one gate for maintenance using the hoist trolley, Williams said. The project includes designing a monorail system to replace the hoist trolley. A monorail system would not just be quicker to use, but safer for the BRA employees doing the work, he said. While the BRA maintenance crew has been able to keep the trolley system operational for many years now, it has obsolete components and needs to be replaced to ensure future reliability.
The evaluations are expected to be done in less than two years. At that time, the BRA will determine a path forward.
Maintaining the dam structure is of utmost priority and critical to the BRA. The project is a continuation of ongoing and regular maintenance and repairs existing at the reservoir.